A transfer device comprises a base on which a workpiece carriage is slidably mounted for movement to successive work stations. The carriage in turn supports workpiece gripping fingers. Such transfer devices are disclosed, for example, in U.S. Pat. Nos. 3,165,192; 3,411,636 and 4,032,081. Such transfer devices are operated by the ram of a press through an actuator mounted on the carriage for reciprocation along a path parallel to the path of travel of the carriage on the base. The ram drives the actuator and further drives both the carriage and the workpiece engaging fingers through numerous gears. During travel of the actuator, the workpiece engaging fingers are moved inward or outward to engage or disengage a workpiece, depending upon the direction of travel of the actuator, and thereafter, the carriage is shifted on the base laterally with respect to the finger movement through a stroke corresponding to the distance between successive stations.
Such prior transfer devices incorporate a cam and/or a rack and pinion to drive an output shaft to actuate the carriage and work engaging fingers. With prior cam driven transfer devices, only 90.degree. rotation of the output shaft was possible to drive the carriage and the work engaging fingers. As a result, the work engaging fingers, for example, start moving at a slow acceleration and end movement at the highest velocity resulting in high impact forces between the fingers and the workpieces. This produces wear of parts and subjects the device to shock with the possibility of damage. Rack and pinion drives allow 180.degree. shaft rotation resulting in carriage and finger motion starting at a slow acceleration and decelerating at the end of movement to avoid backlash and high inertial forces. However, in order to achieve the 180.degree. rotation, the rack must be excessively long requiring much space and, for example, interferes with changing of the die.
It is therefore a general object of the invention to provide a drive for each a carriage and for work engaging fingers that achieves optimum acceleration and deceleration through its range of motion to avoid damage caused by backlash and high inertial forces, that is an independent stand-alone assembly adapted for use with existing transfer devices, and that is compact and saves space.